RF switch

ABSTRACT

A radio frequency (RF) switch which is used in an RF unit of a communication apparatus and which has less of an insertion loss during a transmission. A strip line disposed in the RF switch is formed by combining first and second strip lines having different values of characteristic impedance from each other.

TECHNICAL FIELD

The present invention relates to a radio frequency (RF) switch used inan RF unit of various communication apparatuses.

BACKGROUND ART

A conventional radio frequency (RF) switch for switching an antenna overa transmitting circuit and a receiving circuit is descried in JapanesePatent Laid Open No. 7-312568. FIG. 5 illustrates an equivalent circuitof the conventional RF switch. As shown in FIG. 5, a diode 524 iscoupled between an antenna 501 and a transmitting circuit 502, and astrip line 540 is coupled between the antenna 501 and a receivingcircuit 503. The anode of a diode 546 is coupled to the strip line 540at the receiving circuit 503 side, and the cathode of the diode 546 isgrounded. A control voltage circuit 530 is coupled to the anode of thediode 524.

When a signal is received, namely, when the diodes 524, 546 are bothturned off, a capacitor between both ends of the diode 546 decreases acharacteristic impedance of the strip line 540 at the receiving circuit503 side. A compensating capacitor 532 is coupled to the strip line 540at the antenna 501 side for compensating for the decreasing of thecharacteristic impedance of the strip line 540.

The compensating capacitor 532 is disposed for the receiving circuit503. When a signal is transmitted, namely, when the diodes 524, 546 areboth turned on, the compensating capacitor 532 becomes an additionalcapacitor that is added on the signal path between the antenna 501 andthe transmitting circuit 502. This increases a loss of the transmittedsignal due to inserting the radio frequency switch.

SUMMARY OF THE INVENTION

A radio frequency (RF) switch is provided which causes less of aninsertion loss during transmission. A strip line that is disposed in theRF switch is formed by a combination of two strip lines having differentcharacteristic impedances from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit diagram of a radio frequency (RF) switchin accordance with an exemplary embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of an RF switch module employingthe RF switch in accordance with the exemplary embodiment of the presentinvention.

FIG. 3 is a perspective view of a lamination-type RF switch module whichis formed by laminating the RF switch modules in accordance with theexemplary embodiment of the present invention.

FIG. 4 is an exposed perspective view of the lamination-type RF switchmodule shown in FIG. 3.

FIG. 5 is an equivalent circuit diagram of a conventional RF switch.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary embodiment of the present invention will be describedhereinafter with reference to the accompanying drawings.

FIG. 1 is an equivalent circuit diagram of a radio frequency (RF) switchwhich is used in an RF unit of a communication apparatus such as aportable telephone. The RF switch is a single-port-double-terminal(SPDT) type RF switch for selectively coupling an antenna 101 to one ofa transmitting circuit 102 and a receiving circuit 103.

The RF switch comprises:

(a) a diode D₁ of which the anode is coupled to the transmitting circuit102, and of which the cathode is coupled to the antenna 101;

(b) a controller 104 which is coupled to the anode of diode D₁;

(c) a strip line L of substantially one-fourth the /4 wavelength of atransmission frequency in the transmitting circuit 102, wherein one endof the strip line L is coupled to the connection of the diode D₁ and theantenna 101, and the other end of the strip line L is coupled to thereceiving circuit 103; and

(d) a diode D₂ of which the anode is coupled to a connection of thestrip line L and the receiving circuit 103, and of which the cathode isgrounded.

When a signal is transmitted, a positive voltage that is applied fromthe controller 104 turns on both diodes D₁ and D₂. Thus, the receivingcircuit 103 side of the strip line L is grounded via the turned-on diodeD₂, and the receiving circuit 103 side that is observed from antenna 101is opened. In addition, the transmitting circuit 102 is coupled to theantenna 101 via the turned-on diode D₁, and the transmitted signal whichis fed from the transmitting circuit 102 is thus supplied to the antenna101.

When a signal is received at the antenna 101, a positive voltage is notapplied from the controller 104 to turn off both diodes D₁ and D₂.Because the turned-off diode D₁ disconnects the antenna 101 to thetransmitting circuit 102, the received signal which is fed from theantenna 101 is supplied to the receiving circuit 103. When a signal isreceived, i.e., when the diode D₂ is turned off, a capacitor betweenboth ends of the diode D₂ makes a characteristic impedance of the stripline L at the receiving circuit 103 side lower than that at the antenna101 side. A capacitor C₁ compensates a balance of the characteristicimpedances at both ends of the strip line L.

The strip line L is formed by two, series-interconnected strip lines L₁and L₂ having different characteristic impedances from each other. Thecombination of the characteristic impedances of strip lines L₁ and L₂can determine a desired characteristic impedance of the strip line L.Therefore, the balance of the characteristic impedances at both ends ofthe strip line L is arbitrarily adjusted by determining thecharacteristic impedances of the strip lines L₁ and L₂. As a result, thecapacitance of the compensating capacitor C₁ can be set to a value whichis suitable for a transmission path during the transmission. Further, aninsertion loss of the RF switch during the transmission is thussuppressed.

For example, when the strip lines L₁ and L₂ are combined, and when thecapacitance of the compensating capacitor C₁ is adequately selected, thecapacitor C₁ can cancel an inductance of the diode D₁, where theinductance is contained in the transmission path during thetransmission.

The capacitor C₁ also prevents the capacity between the ends of thediode D₁ from decreasing the characteristic impedance of the strip lineL at the receiving circuit 103 side when the diode D₂ is turned offduring the reception of a signal. When the characteristic impedance ofthe strip line L₂ at the receiving circuit 103 side is set higher thanthe characteristic impedance of the strip line L₁ at the antenna 101side, the capacitance of capacitor C₁ can be reduced. When thecharacteristic impedance of the strip line L₁ is particularly set tosubstantially 50 ohms, the compensating capacitor C₁ can be omitted.

When the characteristic impedance of the strip line L₂ is set higherthan the characteristic impedance of the strip line L₁, the strip line Lhas a stepped impedance resonator (SIR) structure whose one end isshort-circuited during the transmission. Therefore, a solid line lengthof the strip line L is extremely reduced, the receiving path during thereception is shortened, and the insertion loss of the RF switch duringthe reception is accordingly suppressed.

Capacitors C₂ at the respective ends of the antenna 101, thetransmitting circuit 102, and the receiving circuit 103 cut a directcurrent (DC) component of the positive voltage that is applied from thecontroller 104.

FIG. 2 is an equivalent circuit diagram of an RF switch module in whicha low pass filter (LPF) 201 is coupled to the transmitting circuit sideof an RF switch 202 as discussed above. FIG. 3 is a perspective view ofa lamination-type RF switch module which is formed by laminating theequivalent circuit of the diagram.

As shown in FIG. 3, the lamination-type RF switch module includes anantenna terminal electrode 2, a transmitting terminal electrode 3, areceiving terminal electrode 4, a control voltage terminal electrode 5,and a grounding terminal electrode 6 disposed in the outer side-surfacesof the layered body 1 which is made of dielectrics. Chip diodes 7, 8 anda chip inductor 9 are disposed on the upper surface of layered body 1.

The layered body 1, as shown in FIG. 4, comprises dielectric sheets 10 a–10 k. Grounding electrodes 11 a, 11 b are respectively disposed on thesubstantially entire surfaces of the dielectric sheets 10 a, 10 c. Agrounding electrode 11 c is disposed on the right part of the dielectricsheet 10 f.

Capacitor electrodes 12, 13, 14, 15 a, 15 b, which are provided forgrounding, are disposed on the dielectric sheet 10 b. Facing to thegrounding electrodes 11 a and 11 b, the electrode 12 forms capacitor C₄in FIG. 2, the electrode 13 forms the capacitor C₃ in FIG. 2, one ofwhich ends is connected to control voltage terminal electrode 5, theelectrode 14 forms the capacitor C₁ in FIG. 2, one of which ends isconnected to the antenna terminal electrode 2, the electrode 15 a formsthe capacitor C₅ in FIG. 2, and the electrode 15 b forms the capacitorC₆ in FIG. 2, one of which ends is connected to the transmittingterminal electrode 3, respectively.

Strip line 16, as an inductor L₃ in FIG. 2, one of which ends isconnected to the transmitting terminal electrode 3, and strip line 17 a,as an inductor L₂ in FIG. 2, one of which ends is connected to receivingterminal electrode 4, are disposed on the dielectric sheet 10 d.

Strip line 17 b, as an inductor L₁ in FIG. 2, one of which ends isconnected to a strip line 17 a through a via hole 18, is disposed on thedielectric sheet 10 e. Capacitor electrode 19, which forms the capacitorC₅ in FIG. 2, one of which ends is connected to the transmittingterminal electrode 3, is disposed at the left side of the strip line 17b.

Capacitor electrodes 20, 21, 22 are disposed on the left parts in thedielectric sheets 10 f, 10 g, 10 h. Facing to the electrodes 20 and 22,the electrode 21 forms the capacitor C₃ in FIG. 2. Facing to theelectrodes 19, the electrode 20 forms the capacitor C₄ in FIG. 2.

Strip line 23, which forms the strip line L₄ in FIG. 2, one of whichends is connected to grounding terminal electrode 6, is disposed on thedielectric sheet 10 i. Strip line 24, which forms the strip line L₅ inFIG. 2, one of which ends is connected to the control voltage terminalelectrode 5, is disposed at the left side of the strip line 23.

Mounting electrodes 25 a, 25 b, 25 c, 25 d for mounting chip diodes 7, 8and mounting electrodes 26 a, 26 b for mounting chip inductor 9 areformed on the dielectric sheet 10 k.

The mounting electrode 25 a side of the chip diode 7, diode D₂ in FIG.2, is coupled to the connection electrode 28 through the via hole 27,and to the strip line 23 and the capacitor electrode 12 through the viahole 29. The mounting electrode 25 b side of chip diode 7 is coupled tothe receiving terminal electrode 4 through the via hole 30 and theconnection electrode 31.

The mounting electrode 25 c side of the chip diode 8, diode D₁ in FIG.2, is coupled to the connection electrode 33 through the via hole 32,and to the strip line 24, the capacitor electrode 22, the capacitorelectrode 20, the strip line 16, and the capacitor electrode 15 bthrough the via hole 34. The mounting electrode 25 d side of the chipdiode 8 is coupled to the antenna terminal electrode 2 through the viahole 35 and the connection electrode 36. The electrode 36 is coupled toan end of the strip line 17 b through via the hole 37.

The mounting electrode 26 a side of the chip diode 9, inductor L₆ inFIG. 2, is coupled to the connection electrode 39 through the via hole38, and to the capacitor electrode 21 through the via hole 40. Themounting electrode 26 b side of the chip diode 9 is coupled to theantenna terminal electrode 2 through the via hole 41 and the connectionelectrode 36.

A respective thickness of the dielectric sheets 10 f, 10 d which areshown in FIG. 4 differs from each other so as to make a respectivecharacteristic impedance of the strip lines L₁ and L₂ differ from eachother. Strip line 17 a, strip line L₁ in FIG. 2, is disposed on thelower surface of the dielectric sheet 10 f, and the grounding electrode11 c is disposed on the upper surface of the dielectric sheet 10 f.Strip line 17 b, strip line L₂ in FIG. 2, is disposed on the uppersurface of the dielectric sheet 10 d, and the grounding electrode 11 bis disposed on the lower surface of the dielectric sheet 10 d. Thecharacteristic impedance of the strip line 17 a is determined by aninterval between the strip line 17 a and the grounding electrode 11 b,and the characteristic impedance of strip line 17 b is determined by aninterval between the strip line 17 b and the grounding electrode 11 c.Accordingly, a desired characteristic impedance of each of the striplines 17 a and 17 b can be obtained by adjusting the thickness of eachof the dielectric sheets 10 d and 10 f.

Actually, the thickness of the dielectric sheet 10 f is made thinnerthan the thickness of the dielectric sheet 10 d, and the characteristicimpedance of strip line 17 a is accordingly set higher than thecharacteristic impedance of the strip line 17 b. As discussed above, thecapacitance of the correcting capacitor C₁ can be reduced, and aninsertion loss of the RF switch during the transmission is thussuppressed.

The characteristic impedances of the strip lines 17 a, 17 b differingfrom each other are also obtained by making the line widths thereofdifferent from each other. The same effect can be obtained by formingthe strip lines 17 a, 17 b on a common layer, e.g., the dielectric sheet10 d, and changing the line width in a single strip line such as thestrip line 17 a at the intermediate portion of the single strip line.Also, a combination of the changing of the line width and the differingof the thickness of the dielectric sheets 10 d, 10 f can adjust thecharacteristic impedance.

The strip lines 17 a, 17 b are connected through the via hole 18.Because the electric characteristic of the via hole 18, namely, Q value,is higher than electric characteristic of an electrode pattern or thelike that is formed on side surfaces of the layered product, theincreasing of the insertion loss of the RF switch at this part issuppressed.

INDUSTRIAL APPLICABILITY

The present invention relates to a radio frequency (RF) switch which isused in an RF unit of various communication apparatuses and provides theRF switch with a less insertion loss during a transmission. The RFswitch includes a strip line that is formed by combining two strip lineshaving different characteristic impedances.

1. A radio frequency switch for coupling an antenna selectively to oneof a transmitting circuit and a receiving circuit, comprising: a firstdiode coupled between the antenna and the transmitting circuit; a stripline coupled between the antenna and the receiving circuit; a seconddiode coupled between the receiving circuit and a ground; and acontroller for controlling said first and second diodes to be turned onor off; wherein said strip line includes a first strip line having afirst end and a second end, said first end of said first strip linebeing connected with the antenna, and a second strip line having a firstend and a second end, said first end of said second strip line beingconnected with said second end of said first strip line, and said secondend of said second strip line being connected with the receivingcircuit; and wherein a characteristic impedance of said second stripline is higher than a characteristic impedance of said first strip line.2. The radio frequency switch according to claim 1, wherein thecharacteristic impedance of said first strip line is substantially 50ohms.
 3. A radio frequency switch comprising: a layered body formed bylaminating a plurality of dielectric sheets; an antenna terminalelectrode disposed on an outer surface of said layered body; atransmitting terminal electrode disposed on the outer surface of saidlayered body; a receiving terminal electrode disposed on the outersurface of said layered body; a grounding electrode disposed in saidlayered body; a first diode disposed on said layered body and coupledbetween said antenna terminal electrode and said transmitting terminalelectrode; a strip line disposed in said layered body and coupledbetween said antenna terminal electrode and said receiving terminalelectrode; and a second diode disposed on said layered body and coupledbetween said receiving terminal electrode and said grounding electrode;wherein said strip line includes a first strip line having a first endand a second end, said first end of said first strip line beingconnected with the antenna terminal, and a second strip line having afirst end and a second end, said first end of said second strip linebeing connected with said second end of said first strip line, and saidsecond end of said second strip line being connected with the receivingterminal; and wherein a characteristic impedance of said second stripline is higher than a characteristic impedance of said first strip line.4. The radio frequency switch according to claim 3, wherein line widthsof said first and second strip lines differ from each other.
 5. Theradio frequency switch according to claim 3, wherein said first andsecond strip lines are respectively disposed on different dielectricsheets of the plurality of dielectric sheets in said layered body. 6.The radio frequency switch according to claim 3, wherein line widths ofsaid first and second strip lines differ from each other, and said firstand second strip lines are respectively disposed on different dielectricsheets of the plurality of dielectric sheets in said layered body. 7.The radio frequency switch according to claim 3, wherein an intervalbetween said first strip line and said grounding electrode differs froman interval between said second strip line and said grounding electrode.8. The radio frequency switch according to claim 3, wherein said firstand second strip lines are respectively disposed on different dielectricsheets of the plurality of dielectric sheets in said layered body andcoupled to each other through a via hole.